1. Field of the Invention
The present invention relates to a method of measuring a rheological property of a composite filled with particles obtained by mixing and dispersing a particulate material in a liquid material such as resin and equipment therefor. In more particularly, it relates to a method for measuring a rheological property of a composite filled with particles and evaluation equipment employing, and this method comprises a method wherein a rheological property of a composite filled with particles obtained by mixing a raw-material particulate material with a liquid material is measured in situ in a condition maintaining the original material structure without destroying the material by applying external force such as shearing force thereto, by measuring as an anisotropy signal the coagulation structure of the particulate material within the composite filled with particles, and using the amount of this anisotropy as an index of a rheological property, of the properties of the composite filled with particles.
2. Description of the Related Art
Composite materials filled with particles obtained by mixing and dispersing particulate materials in liquid materials such as resins are employed as insulating materials, electrode/conductive materials, electroviscous fluids, chemical/mechanical grinding slurries, and raw materials for ceramic molding processes such as injection molding and/or cast molding, and also, in recent years, have come to be widely used in sealing materials intended for protecting and insulating semiconductor elements. In particular, with progress in VLSI, in order to achieve increased element fineness, low viscosity/high forming ability of composite materials filled with particles in order to achieve the ability to produce any required shape and/or to enable pouring between minute electrodes is indispensable.
However, scientific study of the field of such composite materials filled with particles is still in its infancy and studies relating to the viscosity and moldability of composite materials filled with particles are based merely on experience. For example, in common methods of evaluation of the rheological properties such as viscosity of a composite filled with particles, this is evaluated indirectly by deduction from primary information such as the particle size distribution of the particulate material constituting the raw material for packing/dispersion. Such methods of evaluation are based on the fact that the viscosity of the particle dispersion material becomes smaller as the particle size of the particulate material that is mixed therein becomes large and the relative surface area becomes small, or that the viscosity becomes lower as the width of the particle size distribution becomes greater. However, in current practically used material systems, products are seldom prepared wherein these factors are individually controlled and owing to the complex mutual interaction of various factors, it is difficult to define conditions such that rheological properties are dominant. It has therefore been pointed out that there are limits to the extent to which it is possible to achieve the accuracy required in an evaluation technique of rheological properties of for example semiconductor sealing materials simply using such conventional discoveries (for example, Shinsuke Hagiwara xe2x80x9cThe present state of development of semiconductor sealing materialsxe2x80x9d, Plastics, Vol. 49, p. 58, 1998 and Takeshi Kitano xe2x80x9cRheological properties of filler packing polymer meltsxe2x80x9d, Filler, Vol. 3, p. 96, 1998).
As a way of solving this, attempts have been made to construct theoretical hypotheses of the packing structure and dispersion condition of the particulate material in the composite filled with particles, and to correlate these with rheological properties. For example, in the field of wet molding of ceramics there are studies of slurry viscosity hypothesizing the particle structures formed in the molding process (for example, Laid-open Japanese Patent Publication Number 11-304686 (1999) and Ichiro Tsubaki et al. xe2x80x9cNew method of evaluation of slurries for optimal design of wet molding processesxe2x80x9d, Journal of the Ceramics Association of Japan (Nippon Seramikusu Gakkai Ronbunshi), Vol. 106, p. 504, 1998). Also, in the field of electroviscous fluids, there are attempts to correlate the relationships between density and current values of mixed particulate materials (for example Laid-open Japanese Patent Publication Number 11-343496 (1999)). Although there are instances where methods such as the above succeed in the case of material systems where the concentration of the particulate material is not particularly large, so that the particle size distribution etc. is simple (if possible monodispersed), they cannot adequately cope with dispersed systems of high particulate material concentration having practically employed particle size distribution and/or surface characteristics (for example, Hiroki Usui xe2x80x9cRheological model for coagulated slurry of monodispersed fine silica particlesxe2x80x9d, Collected Chemical Engineering Papers (Kagaku Kogaku Ronbunshu), Vol, 25, p. 459, 1999)
We have up to the present been unsuccessful in finding any studies in which the secondary structure of particulate materials as described above is actually directly observed in the condition in which the composite filled with particles is employed i.e. in a condition in which the original material structure is maintained. We believe that one reason for this is that no method has been established for observing the internal structure of a dispersion system and correlating this structure with its properties when the liquid material is a dispersion medium. For example, there is the problem that no methodology has been prepared for the application to liquid material systems of methods of measurement using X-ray diffraction equipment, optical microscopes, or scanning electron microscopes (SEM) etc., which are the universal methods in the case of dispersion systems where the dispersion medium of the particulate material is solid (for example ceramic material systems etc.).
Also, in most existing methods of measuring rheological properties, measurement was effected by inserting a stirrer or cantilever of an interatomic force microscope into the composite filled with particles, thereby destroying its structure, and using the shearing force etc. when this was done as an index. Methods existed in which structural analysis was conducted in a non-contacting condition with the composite filled with particles still in the condition in which it is actually used, by employing an electron beam or X-ray diffraction, in the case of the particulate material on its own, or by employing polarization or interference of light waves, in the case of the liquid material on its own. However, no method employing these has been found in the case of a composite filled with particles, which is a material in which these are mixed together. The case when the liquid material is a resin-based material can be regarded as one type of polymer material. In polymeric material systems, typically use is made of polarized light observation for evaluation of the photoelasticity characteristic with applied stress, measurement of the birefringence of a plastic lens, or evaluation of molecular alignment characteristics in liquid crystal materials. However, no attempts have been made to employ this for evaluation of the characteristics of particles, rather than resin, in resin composite materials filled with particlesxc2x7dispersion materials. The reason for this is believed to be that the particulate materials that are generally employed in this material field are amorphous SiO2 particles and it was not intuitively anticipated that these methods of observation could be applied to materials having an isotropic crystalline structure (or not having a crystalline structure).
In order to overcome the defects possessed by such conventional measurement techniques for composite materials filled with particles, the present invention was developed taking as technical problem the provision of a method of measurement of rheological properties of composite materials filled with particles and evaluation equipment employing this principle of measurement under the following necessary conditions: in situ measurement of the rheological property of the composite filled with particles in a condition in which the original material structure is maintained without destroying the material by applying external force such as shearing force; measurement of non-uniform structure i.e. coagulation structure of the particulate material within the composite filled with particles as an anisotropy signal; and employment of the amount of this anisotropy as an index of the rheological property value of the composite filled with particles properties.
The present inventors noted that when a composite filled with particles was prepared the packing structure of the particulate material became non-uniform or, when secondary coagulation was created, the alignment of the polymers was increased by application of stress to the surrounding liquid material compared with regions where such stress was not applied. Also, it was thought that bubbles might be produced in the region of the interface between the particulate material and the liquid material, or the interface itself (connection surface of different refractive indices) constituted by the materials of different types might constitute an optically anisotropic body. It was conceived that it should be possible to measure rheological properties of composite materials filled with particles, as these would provide structures capable of being detected by crystallographic measurement methods or optical distortion, offering the possibility of performing evaluation by observation at diagonally opposite positions, and as it was thought that the (apparent) density of the particulate material would be raised by inclusion of liquid material in the packing/dispersion structure of the particulate material or that constituents of the dispersion medium not contributing to shearing would be increased on the manifestation of viscosity.
As a result of various studies aimed at implementing the above concept concerning the effect of primary characteristics of the particles such as the particle size distribution of the particulate material used as filler, the method of preparation and the evaluation test conditions etc., the present inventors discovered that non-uniform structure of a composite filled with particles could be measured by utilizing the optical anisotropy or crystallographic anisotropy possessed by the liquid material or the particle/liquid interface and that the packing structure or condition of dispersion of the particulate material could be identified using the results of such measurement as an index i.e. that there was a unique correlation of the condition of dispersion of the fine particles measured in terms of the aforesaid anisotropy with the rheological properties of the composite filled with particles, and perfected the present invention based on this discovery.
There is provided a measurement technique for rheological properties of a composite filled with particles and evaluation equipment using this.
This invention relates to a method of measuring a rheological property of a composite filled with particles, and evaluation equipment, in which in situ measurement is performed of the rheological property of a composite filled with particles obtained by mixing a particulate material as raw material with a liquid material, in a condition with the original material structure maintained, without destroying the material by applying external force such as shearing force thereto, comprising a step of measuring the coagulation structure of the particulate material within the composite filled with particles as an anisotropy signal, and a step of employing the amount of this anisotropy as an index of the rheological property value of the composite. This is beneficial in particular as a method of evaluation of semiconductor sealing material/manufacturing process control technique in that it makes it possible to provide a method of in situ measurement and evaluation equipment therefor in a condition in which the original material structure is maintained without destroying the material by applying external force such as shearing force to the composite filled with particles or without performing special processing.
An object of the present invention is to provide a method and evaluation equipment using the method for measuring a rheological property of a composite filled with particles in a non-contacting condition with the measurement means with the composite filled with particles still in the condition in which it is actually used by identifying the dispersion condition of the particulate material and liquid material using as an index the result of measurement achieved by actual measurement and detection of the packing structure and/or dispersion condition of the particulate material in the composite filled with particles by utilizing optical anisotropy or crystallographic anisotropy possessed by the liquid material and/or particle/liquid interface, which was hitherto only capable of being theoretically hypothesized.
In order to realize the above object, according to the present invention, the following constitution is adopted:
(1) A method of measuring a rheological property of a composite filled with particles in which in situ measurement is performed of the rheological property of a composite filled with particles obtained by mixing a particulate material as raw material with a liquid material, in a condition with the original material structure maintained, without destroying the material by applying external force such as shearing force thereto, which comprises a step of measuring the coagulation structure of the particulate material within the composite filled with particles as an anisotropy signal, and a step of employing the amount of this anisotropy as an index of the rheological property value of the composite material.
(2) The method of measuring a rheological property of a composite filled with particles according to (1) above, wherein the coagulation structure of the particulate material is measured by utilizing crystallographic or optical anisotropy obtained using diffraction of electron beam or X-ray, or polarization/interference of light waves.
(3) The method of measuring a rheological property of a composite filled with particles according to (1) above, wherein the coagulation structure of the particulate material is measured by utilizing photoelasticity based on local rearrangement of liquid material molecules, or the difference of refractive indices of the particulate material and the liquid material.
(4) The method of measuring a rheological property of a composite filled with particles according to (1), (2) or (3) above, wherein the particulate material is an SiO2-based material or AlN-based material.
(5) The method of measuring a rheological property of a composite filled with particles according to (1), (2) or (3) above, wherein the liquid material is a resin-based material.
(6) Equipment for measuring and evaluating a rheological property of a composite filled with particles, which is used in the method of measurement claimed in any of (1) to (5) above, which comprises as structural elements two polarizing elements, a light source or electron beam source, means for observing a transmitted image, and means for arranging a sample,
wherein a thin strip sample for transmission observation is arranged between the two polarizing elements, monochromatic light polarized by the first polarizing element is directed onto the sample, and subjected to double refraction at optically anisotropic regions such as coagulations in the sample, then re-polarized by the second polarizing element, and observed by the transmitted image observation means to measure and evaluateoptical behavior thereof such as diagonally opposite positions or interference.
(7) The equipment for evaluation according to (6) above, wherein the sample is a composite filled with particles produced in thin strip form of a thickness allowing monochromatic light from a light source or electron beam source to be transmitted through the composite.
(8) The equipment for evaluation according to (6) above, wherein halogen light is directed on the sample.